Transparent proxy config

Hi all, I'm new to siproxd, I wanted to test the transparent proxy
config (as found in the online doc). But between a public machine and a
remote LAN, as explained below:


+-------------+                   +--------------+
!             !publicIP  publicIP ! masquerading ! publicIP                 Remote LAN
! SIP GW      !-------------------! Firewall     !------>>  (IP tunnel) --- 10.x.x.x
!             !                   ! siproxd      !
+-------------+                   +--------------+
                                  eth2   :  eth3


The SIP GW sends INVITEs to a SIP server via my masquerading firewall
through the public Internet. When the call gets established I'd like
siproxd to relay the RTP between the private (remote) LAN and the public
GW.

With the example config, I get "Outgoing Call from:
*NULL*@212.62.110.65" errors when my public GW (212.62.110.65) tries to
send INVITEs to the server behind the firewall. 

Is my config possible? How can I do it with siproxd?
Thanks a lot for your help!

-- 
Alexandre Aractingi <[email protected]>